This invention relates to a weigh scale. More particularly, this invention relates to an industrial, low-profile, non-platform type of weigh scale adapted to rest on a building floor or the like and particularly suited for weighing loads carried on pallets.
Many kinds of items and materials are handled and transported regularly in all types, kinds and fields of industry. A great deal of industrial handling is performed using pallets for loading thereon various items and moving the loaded pallets by powered fork-lift trucks and lower-cost manually-operated pallet movers. It is often convenient to determine the weight of the palletized material at some time during handling. Conventionally, scales used for the purpose of weighing items and materials handled in industry have been essentially three types:
The first is weigh scales which are connected directly to the powered fork-lift trucks. Normally, the scale either rests on the forks of the fork-lift truck or is incorporated into the fork-lift mechanism of the truck by using hydraulic cylinders. Having the scale incorporated in the fork lift of the powered fork-lift truck allows weights to be taken each time an item is lifted. However, the significant disadvantage of this type of weigh scale is that it is fixed to the fork-lift truck and thus requires operation of that particular powered truck for weighing all the necessary materials that have to be handled. This would thus require fitting of weigh scales on all fork-lift trucks, or would require only one operator of a fork-lift truck to achieve all the weighing of the handled material and thus likely limit use of the powered fork-lift truck for other non-weighing operations. Moreover, it can require a costly and complicated assembly of the weigh scale to be part of the truck itself. Finally, this type of weigh scale does not always provide an accurate weigh measurement due to the necessity of placing the load onto two parallel forks of a moving vehicle and the instability thereof when measurement occurs.
There are other scales which have been incorporated onto fork-lift trucks and they are made up of scale beams connected to the sides of the truck which are swung into operating position once the fork lift raises the load to a point above the horizontal plane of the scale beams. After weighing, the load is again raised to allow the scale beams to be swung into the non-operating position. Of course, the time needed to swing the scale beams between every weight measurement is a major disadvantage. This scale also suffers from the disadvantages discussed above.
Such systems assembled to fork-lift trucks and movers are shown in U.S. Pat. Nos. 2,638,336, 2,940,746, and 3,431,992.
The second type of scale is concerned with weigh scales of a platform-type which require construction of a "pit" in the building floor to house the operating mechanism. The platform is more or less flush with the surrounding floor or road area to enable powered fork-lift trucks or the manually-operable pallet movers to drive onto the platform with the load to be weighed.
In the normal operation of such scales, a fork-lift truck and the load resting on the pallet are weighed together. This weight is then substracted from the known or tare weight of the fork-lift truck and the operator so that the weight of the load alone can be determined. The major disadvantage to this operation is that it leads to inaccurate weight measurements, especially when the weight of the load is far lighter than the truck. Also, for example, if the fork-lift truck operator who was involved in the weighing of the fork-lift truck alone is different from the operator who later performs the weighing of the truck, pallet and load, the different weights of the operators could cause a degree of inaccuracy in the weighing. Similarly, different amounts of fuel in the fuel tank of the vehicle could affect the weighing accuracy. To remedy the above inaccuracies, the tare weight of the fork-lift truck and operator could be determined just before each weighing of the truck, pallet and load. However, this would greatly increase the overall time required for taking weight measurements. Alternatively, the truck or pallet mover used to move the load onto the platform can be removed from the platform each time a measurement is to be taken. Once a measurement is taken, the truck or pallet mover would then be moved back onto the platform to remove the weighed load. Of course, while this may ensure a more accurate weight measurement, the overall time required for taking weight measurements is greatly increased.
The above type of "pit" platform scale is briefly discussed in U.S. Pat. No. 3,472,329. It can be seen that the "pit" platform scale is a permanent weigh scale, requires expensive construction, and requires a very time-consuming operation of either weighing the truck both with and without the load, or by driving the truck or pallet mover with the loaded pallet onto the platform of the weigh scale, unloading the palletized items onto the platform, driving off the platform and then driving back onto the platform after the weighing operation has been achieved.
The third type of weigh scale is a drive-on elevated platform type of scale constructed to rest on the building floor or the like, but does not require a "pit." The scale comprises a platform and suspension-type load cell assembly made up of columns of strain gauge load cells and short lengths of suitable flexible connector, such as steel strand cable. For stabilizing the weigh platform from side forces, transverse and longitudinal check links are provided. The side frame members of the scale extend above the drive-on platform and necessarily are the height of the platform plus the height of the suspension-type load cell assembly, making the total height of the scale about twice the size of the load cell. This type of platform has a ramp positioned at at least one end of the platform to enable a fork-lift truck to drive onto the weighing platform and thus the scale normally requires secure anchoring to the floor. The above type of elevated platform scale is shown in U.S. Pat. No. 3,472,329. This scale appears to require use of a powered fork-lift truck to move the item onto the platform instead of a manually-operable pallet mover because of the steepness of the ramp. Again, as with platform scales requiring a "pit," in order to weigh the load, the truck usually is weighed alone first and compared to the weight of the truck, pallet and load. However, as stated above, this process is both inaccurate and time-consuming. Alternatively, once the load to be weighed is positioned on the platform, it is possible that the load mover be removed in order to perform the weighing measurement. However, this weigh procedure for the scale is also a very time-consuming operation.
Industrial weigh scales should be simple in construction, economical, efficient, versatile, and accurate. These goals are achieved by scales which, inter alia:
(1) have the least original investment, e.g., those which do not require the construction of a "pit" or the use of expensive, powered fork-lift trucks;
(2) do not require the extra time needed to weigh the truck alone first without the load, to move scale beams connected to the fork truck into operating position or to remove the item mover from the scale between each weighing measurement;
(3) have the least amount of mechanical parts by not employing an elaborate platform suspension assembly, thereby reducing costs and ensuring a long-lasting weigh scale;
(4) do not require anchoring to the floor, thereby facilitating portability;
(5) are stable and accurate by employing a configuration of top force-receiving shear beam load cells which function even on an uneven surface and which do not require an elaborate suspension mechanism or links;
(6) require the least height by employing top force-receiving shear beam load cells supporting the upper surface of the scale without an elaborate suspension mechanism; and
(7) do not require a pallet mover to be powered in order to move heavy loads up ramps leading to an elevated platform of a scale.